
Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
Oxygen evolving complex
Introduction

The oxygen evolving complex (OEC) is a water oxidizing enzyme involved in the photooxidation of water during the light reactions of photosynthesis. Based on a widely accepted theory from 1970 by Kok, the complex can exist in 5 states: S0 to S4. Photons trapped by photosystem II move the system from state S0 to S4. S4 is unstable and reacts with water to produce free oxygen. Currently the functional mechanism of the complex is not completely understood. Much of the known data have been collected from flash experiments, EPR, and X-ray spectroscopy.[1]
The OEC appears to to have a metalloenzyme core containing both manganese and calcium, with the empirical formula for the inorganic core of Mn4Ca1OxCl1–2(HCO3)y. Other characteristics of it have been reviewed; see [2]
